1. Technical Field of the Disclosure
The present invention relates to regenerative air preheaters and particularly to improved radial and circumferential sealing arrangements for effecting seals between the relatively movable portions of the air preheater, namely, the drum containing the matrix of heat exchanging elements and the surrounding housing.
2. Description of the Prior Art
It is typical in fuel burning installations or devices, such as electrical power generating plants, to use regenerative air preheaters for heating the intake air to improve the efficiency of the fuel burning operation. These air preheaters typically include two major components, namely, a generally cylindrical drum having a matrix of heat exchanging elements therein and a surrounding housing having a generally cylindrical opening therein. One type of preheater has a stationary drum and a movable housing surrounding the drum. However, the most commonly used preheaters are those of the Ljungstrom type in which the drum is a cylindrical rotor containing metallic heat transfer plates, the rotor being movable with respect to a surrounding stationary housing. As the rotor turns, the heat transfer plates are first exposed to hot discharge gases, and these heated plates then move into the air intake passage to heat the incoming air. The housing surrounding the drum includes sector plates which divide the housing into an air intake half and gas discharge half. In an attempt to reduce the mingling of the two fluids, the drum is typically provided with radially extending seal plates that are intended to pass closely by the sector plates with only a small clearance. Similarly, in a further attempt to reduce mingling of fluids and to reduce the bypassing of air and gas around the periphery of the drum, it is also known to provide circumferential seal plates. Again, these seal plates are intended to pass closely by an annular member on the housing with a small clearance. Also, axial seals between the circumferential seal plates have been used in an apparent effort to reduce leakage which still occurs when circumferential seal plates are used.
A major problem with the foregoing sealing arrangement is that it depends on achieving small, constant and predictable clearances between the seal plates and adjacent surfaces. Such clearances are difficult to attain even in a newly manufactured air preheater, and are particularly difficult to maintain in an air preheater that is in service. Air preheaters, when in service, are subject to extremes in temperature and a very hostile environment. Factors such as wear, distortion of parts due to temperature differentials, normal dimensional changes due to heating and cooling, lack of flatness in the sector plates, out of roundness of the drum and/or adjacent housing portion, and various other factors contribute, in practice, to wide variation in the clearances between moving parts. Excessive clearances of three-quarters of an inch have been known as well as a complete lack of clearance in which there is an unintentional clashing of the metal seal plates with the adjacent sealing surfaces. These problems are further aggravated by the hostile environment to which an air preheater is subjected. The dirty, soot- and acid-laden discharge gas which passes through the air preheater results in soot buildup, corrosion, and wear, all of which contributes to irregularities in the relatively movable parts. The irregularities, of course, lead to sealing difficulties.